Packaging materials for liquid packages consisting of board or cardboard laminated with thermoplastic and possibly aluminium foil are normally provided with fold lines, so-called crease lines which are made when the packaging material is in web form. These crease lines are made using creasing tools which normally consist of a male part with bars and a corresponding female part provided with grooves. In conventional creasing, these tools are made of metal, with or without a surface coating. The crease line is made in that the material passes between the male and female parts of the creasing tool and, when both of the tool parts are forced towards one another, the packaging material is broken between the parts so that crease lines occur.
Since the packaging material is forced between the two metal parts of the tool, the material is exposed to quite large stresses and, instead of forming a distinct crease line, the tool may bring about the creation of two folding or crease lines, and may also cause the packaging material in the process to be partly delaminated and thereby weakened. Trials have been carried out in which the entire female part of the tool has been provided with a rubber coating, but because of tensions in the rubber, it has not been possible in this manner to obtain perfect creases. Similarly, it is difficult in this case to obtain a pitch stroke which is constant throughout. The pitch stroke is the packaging length which must always be uniform in order to ensure that all packages have the same volume and size.